I have this issue a lot too. I'll meet a new person and everything is going fine, sometimes they say "Hi" first, sometimes it's me, really just whoever notices the other is online first. And then after awhile, They stop. And I'm the only one saying "Hi" and it gets to the point they never even reply. (Like on skype, and you never get a: "Sorry I left Skype up!" Or anything. Just nothing.)
I always ask myself, "Why?" I get that people change, interests change. But sometimes, even if you've moved on, you don't have to leave everyone behind? You could just let them know how things are now, and they might understand, they might even feel the same way and you will have a common interest again.
Then there's things like; you join a group, sometime passes. And you really start to realize that they don't care about you. It's like when they talk to you, it's to divert you. "Hey, we're obviously talking in private whispers and you are not invited. Ever. But hi. Okay bye." Sometimes, for me anyway, I might not be able to connect 100% with people. We have a common interest, but if I feel a but different about it they push me away? Why can't we have our own opinions and accept it? Or are you THAT bad at friendship?
I've tried to keep friendships alive so many times. But it's a two way thing.
And a lot of the time the friend seems... Dishonest. Like at some point they honestly want nothing to do with you, but will act all nice anyway. What's the point of faking it? Who gains? No one. You're both wasting your time.
For me it's gotten to the point I hardly want to talk to people, myself. At some point it feels so hopeless.
//end rant. Better stop it here. Apologies if it's confusing. Didn't read over.